Various natural and recombinant proteins have pharmaceutical utility. Once they have been purified, separated, and formulated, they can be parenterally administered for various therapeutic indications. However, parenterally administered proteins may be immunogenic, may be relatively water insoluble, and may have a short pharmacological half life. Consequently, it can be difficult to achieve therapeutically useful blood levels of the proteins in patients.
These problems can be overcome by conjugating the proteins to polymers, such as polyethylene glycol. Davis et al., U.S. Pat. No. 4,179,337 disclose conjugating polyethylene glycol (PEG) to proteins such as enzymes and insulin to obtain conjugates having less immunogenic effect than the original proteins and yet still retaining a substantial proportion of their physiological activity. Veronese et al., (Applied Biochem. and Biotech, 11: 141-152, 1985) disclose activating polyethylene glycols with phenyl chloroformates to modify a ribonuclease and a superoxide dimutase. Katre et cil. U.S. Pat. Nos. 4,766,106 and 4,917,888 also disclose solubilizing proteins by polymer conjugation. Likewise, PEG and other polymers can be conjugated to recombinant proteins to reduce immunogenicity and increase half-life. See Nitecki, et al., U.S. Pat. No. 4,902,502, Enzon, Inc., International Application No. PCT/US90/02133, Nishimura et al., European Patent Application 154,316 and Tomasi, International Application Number PCT/US85/02572. For example, interferon alpha-2b is known to be effective for treatment of disease states such as renal cell carcinoma, AIDS-related Kaposi's sarcoma, chronic and acute hepatitis B, chronic and acute non-A, non-B/C hepatitis and hepatitis C. Improvement of the pharmacological half-life of interferon alpha-2b would improve treatment of these conditions.
While preparation of protein-polymer conjugates is beneficial, they cannot be used in a practical manner unless they can be stored for an extended period of time during manufacture and distribution to health care providers. Some protein-polymer conjugates, however, rapidly deteriorate, even in frozen solutions. Lyophilization (also known as freeze-drying) is a process that can render a pharmaceutical in a form that can overcome this deficiency.
Lyophilization is a process whereby water is sublimed from a composition after it is frozen. In this process, pharmaceuticals and biologicals that are relatively unstable in an aqueous solution over a period of time can be placed into dosage containers in an easily processed liquid state, dried without the use of damaging heat and stored in a dried state for extended periods.
Due to the low total mass of active substance in each dose, the formulations of most pharmaceuticals and biologicals, including protein-polymer conjugates, require additional ingredients to protect the active ingredient during the lyophilization process. For example, a pharmaceutical filled into a dosage container as a low-concentration aqueous solution can be susceptible to physical loss during the lyophilization vacuum process or adsorption to the container. A lyophilized formulation often contains bulking ingredients that increase the amount of solid material, as well as cryoprotectants, lyoprotectants and other stabilizers to protect the active component from damage. Which particular formulation will protect a given type of pharmaceutical, however, must be determined empirically.
There is a present need for a formulation suitable to protect protein-polymcr conjugates, and in particular PEG-interferon alpha conjugates, from damage during lyophilization. Such a formulation should allow PEG-interferon alpha-polymer conjugates to maintain their biological activity, physical stability and chemical stability over extended periods of time.